The invention relates to bearings. More particularly, the invention relates to bearings in cryogenic turbopumps.
Various turbomachines are subject to use at cryogenic temperatures. For example, turbopumps are used in rocket propulsion to pump cryogenic liquids such as oxygen, hydrogen, and hydrazine. One exemplary turbopump configuration is shown in U.S. Pat. No. 5,529,464.
Bearing performance is critical to operation of such machines. Often, the machines are subject to a variety of conditions including start-up, shut-down, and other transient operations. For example, the bearings may be configured for lubrication by the working fluid. However, a lack of such fluid in start-up and shut-down conditions may exacerbate asperity contact between bearing surfaces. Accordingly, much development work has gone into bearings for such applications. Among these are the variety of complex foil bearing constructions (e.g., as proposed in U.S. Pat. No. 6,158,893).
Separately, technologies have developed regarding the deposition of so-called diamond-like coatings including diamond-like carbon (DLC) and diamond-like nanocomposite (DLN) coatings. Exemplary DLN coatings are described in U.S. Pat. Nos. 5,352,493, 5,466,431, 5,728,465, 6,200,675, and 6,228,471. Exemplary DLC and DLN coatings and application services are available from Bekaert Dymonics n.v., Zulte, Belgium. Diamond-like coatings are generally amorphous carbon-based coatings with a high hardness and a low coefficient of friction. Exemplary DLC coatings involve a mixture of SP2 and SP3 bonded carbon atoms stabilized by hydrogen. Exemplary DLN coatings involve interpenetrating networks of a-C:H and a-SI:O. The compositional balances and addition of dopants may vary coating properties.